Jib halyard. The standard setu on these boats is a 2 part system. At the upper left of the photo is the wire portion. that ends in a shackle that attaches to the head of the jib.
The line at the bottom left is the other portion, the part you pull on to raise the jib.
The photo doesn't show it, but the line is a long line, long enough to dangle down to the deck, so you can grab the end & hoist the jib. It is tied to that block with a bowline, but the knot is tied so it leaves a "tail" appx 2' long. once you hoist the jib, the tail goes through a cheek block on the mast, back through the block shown, then down to a cleat on the mast, giving you a 3:1.
The smaller 5.0 does not use this system, & really, unless you are in the Olympics, just pull the wrinkles out of the jib & go sailing.
